The invention relates to a laminated pane, in particular a heating or aerial pane, having the features of the preamble of Patent claim 1. In this context, the term laminated panes is intended to mean multilayer transparent panes comprising at least one rigid glass or plastic pane and a thermoplastic adhesion layer adhering thereto.
These features are known, for example, from EP 0 490 723 A1 or DE 195 41 009 A1.
A laminated pane of this type with a large-area coil of silver or copper wires is known from DE-U1-88 00 823. If necessary, the copper wires are to be tin-coated or silver-coated. The end-side tin-coating of bare wires is a conventional preparatory measure if the wire ends are to be electrically and mechanically connected to other components by soft soldering.
In the case of laminated panes which are designed as heating panes, thin tungsten wires are generally used as heating wires, and these are laid on the thermoplastic adhesion layer in straight or wavy form. To ensure good contact between the connection elements or busbars and the heating wires, the busbars used are in each case two copper foil strips which are tin-coated on at least one side. The two metal foil strips which enclose the ends of the heating wires between them and are tin-coated on this side are heated in a suitable way, for example with the aid of a soldering iron, so that the two tin layers fuse together and the tungsten wires are embedded between the two copper foil strips. The introduction of heat at this point should remain as low as possible, so that the thermoplastic film is not unintentionally damaged.
However, it is known that tungsten wires do not form a soldered connection, or form only an inadequate soldered connection, with tin solder alloys. Therefore, in the known laminated panes, the possibility exists that the heating wires will not be in sufficient electrical contact with the metal foil strips after the soldering of the two metal foil strips.
DE-U 94 11 516 has disclosed a heatable laminated glass pane in which changes to the heating wires caused by moisture diffusing in are ruled out or are at least considerably reduced as a result of a layer of an electrically conductive adhesive being arranged between the two metal foil strips. Therefore, in this laminated pane, an electrically conductive adhesion layer replaces the tin solder layer and simultaneously adheres to the wires over the entire cylindrical surface of the wires in the region between the two metal foil strips and produces the electrically conductive connection between the metal foil strips and the wires.
DE-U 298 03 544 has disclosed an electrically heatable laminated glass pane, in which each of the parallel-connected heating wires forms a meandering loop with an uneven number of loop sections extending over the width of the pane. Because of the meandering arrangement of the heating wires and their large effective length, it is possible to use wire materials of lower resistivity than tungsten, for example copper or a copper alloy. Instead of a busbar, the ends of the heating wires which are of the same polarity are brought together at in each case one location and are connected to in each case one current connection element. The material of the heating wires ensures a good soldered connection to the current connection elements. A drawback of this type of laminated pane provided with electrically conductive wires is the need to use a device which resembles a plotter to lay the wires, as this device operates relatively slowly. The wire-laying device which is known from DE 195 41 427 A1, in which a plurality of intermediate thermoplastic films arranged on a drum are provided with the wires simultaneously and at high speed cannot be used, on account of the wires being laid in meandering loops and on account of the inadequate mechanical strength of the copper wire.
DE 42 35 063 A1 and DE 43 32 320 C1 have disclosed laminated glass pane in which metal wires embedded in the thermoplastic adhesion layer are used as an aerial for radio reception. Ribbon cables made from copper in this case preferably serve as connection elements for the aerial wires, which may also consist of tungsten. When connecting the antenna wires to the connection elements, similar difficulties as those encountered with heating panes arise.
DE 44 16 165 A1 has disclosed a radar-absorbing arrangement for window glazing or facade facings which is of double layer structure with a layer which partially reflects electromagnetic radiation and is arranged in the region of the outer layer and a further reflective layer which is arranged in the region of the inner layer, at a spacing of approximately one quarter of the operating wavelength. This arrangement comprises wire-like electric conductor sections which lie parallel to one another and are arranged in a regular geometric pattern. Tungsten wires have proven to be a particularly suitable material for the conductor sections, since their low thickness means that they are scarcely visible in window glazing. For window glazing, it is considered particularly advantageous for the conductor sections to be applied to a plastic film, for example of polyvinyl butyral. Since the conductor sections are not connected to connection elements, in this case the problem of electrical contact-making does not arise.
It is known from DE-A1-197 03 390 to provide wires of iron or unalloyed steel, which are intended for processing into fencing strips and the like, with a conductive and corrosion-resistant coating with a conductive metal, such as copper, nickel, zinc, chromium, tin or tin/lead. Although these wires must indubitably have a high tensile strength, the problem of solderable contact-making and of (visually inconspicuous) installation in a laminated pane does not arise.
The invention is based on the object of avoiding the abovementioned drawbacks and providing composite panes of the type described in the introduction with a wire material which is improved in terms of the surface conductivity and, if appropriate, solderability.
According to the invention, this object is achieved by the feature of patent claim 1. The features of the subclaims specify advantageous refinements of this subject matter.
In the context of the invention, the term busbar is intended to mean not only a ribbon-like electrical conductor connected to a plurality of wires, but also any electrically conductive connection element of any geometric form which is connection to at least one wire which has been laid on the thermoplastic adhesion layer.
Therefore, wires which do not consist of a homogenous material, but rather are of multilayer structure, are used for the laminated pane according to the invention. The different properties of the individual materials can be utilized in a controlled way in this manner. One demand imposed on a wire of this type is that it has sufficient mechanical strength, in particular tensile strength, so that the wires, which are generally only between 10 xcexcm and 70 xcexcm thick, can be processed automatically without difficulty and can be laid on the thermoplastic adhesion layer in straight or wavy form without loops being formed. There is no question of using a greater diameter for the purpose in question, since it would then be impossible to ensure an unimpeded view through the pane.
A second requirement is to establish the electrical resistance which is required for the particular application with the predetermined diameter. For example, to produce a heatable laminated pane, the resistance of the wires, which extend between 2 busbars which lie opposite one another at a distance of approximately 0.5 m to 2 m, must be appropriate for the required heating capacity. And finally, it must be possible to ensure a good electrical and mechanical connection of the wires, in particular by soft soldering, to the busbars.
The multilayer wire which is embedded in the adhesion layer on one surface of a rigid pane consists of a metal which can withstand high mechanical loads, preferably of stainless steel, which is joined to a metal which has a higher conductivity and can be soldered well, preferably copper.
The cross section of a wire of this type therefore has at least two areas of different material properties. A combination of electrically conductive metals of this type represents a parallel circuit of electrical resistances. The individual resistances are dependent on the geometric dimensions and the resistivities. As a result of the ratio between the cross-sectional areas of the metal which can withstand mechanical loads and the metal of higher conductivity being changed, it is possible to adapt the electrical resistance of the wire per unit length to the particular application. In addition to chromium-nickel steel, which has already been mentioned above, by way of example other steel and stainless steel alloys, alloys of chromium/nickel, copper/nickel, nickel/cobalt, titanium and tungsten are also suitable materials for that part of the wire which can withstand mechanical stresses. As well as copper, it is also possible to use other metals which have a good conductivity and can be soldered, such as for example silver, gold, aluminum or alloys of these metals, provided only that it is ensured that there is a good and permanent bond between the two materials of the wire.
The wire may, for example, be a layered strip of two or more layers of interconnected, electrically conductive material. However, it has proved particularly advantageous for the wire to be constructed from a core of the material which can withstand high mechanical stresses and a sheath of the metal of higher conductivity which surrounds this core. This form of wire may be round, elliptical or polygonal in cross section.
The copper coating takes place at a wire diameter of 0.2 to 0.4 mm. These wires are then fine-drawn to the final dimensions. A resistance of at most 150 xcexa9/m with the smallest possible diameter of the coated wire is desired.
In principle, stainless steel wire can be produced particularly well by fine drawing, since the material has a good ductile behaviour. Tests have shown that an authentic stainless steel designated by materials number 1.4306 (International Standard Designation AISI 403 L) is particularly suitable. The fine diameters produced with this material were impossible to achieve with NiCr materials.
Furthermore, in particular copper adheres particularly well to the stainless steel base material after application by electroplating. With certain combinations of materials, hose effects, in which the outer layer of the highly conductive material tears open and then encloses the metal wire core in sections in the manner of a hose without adhering thereto, may occur when fine-drawing wires (i.e. when reducing the wire diameter to the extremely small dimensions desired here). By contrast, given the good adhesion between stainless steel and copper plating, these problems also do not occur during the fine drawing.
The laminated pane according to the invention with multilayer, electrically conductive wires can be designed not only as an electrically heatable pane but also, for example, as an aerial pane. In this case, it is particularly advantageous that the surface conductivity of a wire which consists of a metallic core and a sheath of a more highly conductive metal is greater than that of a homogenous wire. This counteracts the skin effect, in which high-frequency currents flow primarily at the surface of conductors, so that it is possible to produce pane aerials of particularly high quality. If designed suitably, the laminated pane according to the invention can also be used for further applications, for example as a window protecting against electromagnetic radiation.
The use of a metal of good solderability opens up the possibility of soft-soldering the wires to the busbars. Unlike in the prior art, in which generally tungsten wires are simply embedded between two tin-plated copper foils, with the laminated pane according to the invention it is possible to achieve true soldering if suitable busbars are selected. It is also not necessary for the busbars to comprise two metal foils between which the end sections of the wire are embedded; rather, the busbar may comprise a single-layer strip or foil.
In a further advantageous configuration of the laminated pane, the wires are provided with a matt paint. This makes it possible to effectively reduce or even altogether prevent disruptive reflections which emanate from a possibly shiny metallic surface of the wire. During the soldering operation, the paint layer will break open without requiring special measures and does not impede correct soldering of the wires and busbars.
In this case, once again, copper has the advantage over other highly conductive covering layer materials (such as for example silver) that it is itself relatively dark and unobtrusive. Only a very thin layer of paint has to be applied to copper in order for it to be possible for the wire to be fitted in a visually inconspicuous manner in the laminated pane. The thinner the layer of paint can be kept, the thinner the overall finished, painted wire, since, of course, the layer of paint increases the overall diameter of the wire slightly.
Further details and advantages of the subject matter of the invention will emerge, without any restriction being intended, from the drawing of an exemplary embodiment which is based on an electrically heatable laminated pane and from the associated detailed description given below.